1. Field of the Invention
The present disclosure relates to reduction-oxidation (redox) flow cells and, in particular, to rebalance systems that may be utilized in redox flow cells.
2. Description of the Relevant Art
There is an increasing demand for novel and innovative electric power storage systems. Redox batteries have become an attractive means for such energy storage. In certain applications, a redox flow battery may include one or more redox flow cells. Each of the redox flow cells may include positive and negative electrodes disposed in separate half-cell compartments. The two half-cells may be separated by a porous or ion-selective membrane, through which ions are transferred during a redox reaction. Electrolytes (anolyte and catholyte) are flowed through the half-cells as the redox reaction occurs, often with an external pumping system. In this manner, the membrane in a flow cell battery operates in an aqueous electrolyte environment. In some applications, an iron-ion containing aqueous hydrochloric acid solution may be used as the catholyte, while a chromium-ion containing aqueous hydrochloric acid solution may be used as the anolyte. In some applications, a mixture of chromium and iron containing solutions may be used on both sides of the redox cell. The use of mixed reactants eliminates the requirement for a highly-selective membrane since the electrolyte composition of both half cells is identical in the discharged state.
Typically, the charging and discharging of the redox flow battery results in a disparity of states of charge between the two electrolyte solutions. Parasitic reactions competing with the reduction of certain ions may result in formation of unwanted side products. For example, in the case of acidic electrolytes, certain parasitic reactions may generate hydrogen gas.
Therefore, there exists a need to develop a redox cell system that effectively removes or recycles parasitic side products produced during the charge/discharge cycles of a flow cell battery to rebalance the charge states between the two electrolytic solutions.